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IDProjectCategoryView StatusLast Update
0032346CommunityOCCT:Modeling Algorithmspublic2021-05-10 11:34
Reportergeuzaine Assigned Tomsv 
PrioritynormalSeverityminor 
Status newResolutionopen 
PlatformMacOSOS 
Product Version7.5.1 
Summary0032346: Modeling Algorithms - Strange result of intersection
DescriptionDear OCCT team,

I obtain strange results when I apply boolean operations between the two solids (a tapered cylinder and a sphere) contained in the attached BREP file ("two_volumes.brep").

For example, computing the intersection (BRepAlgoAPI_Common) leads to a self-overlapping spherical patch with loops on the bounding curves (see attached screeenshot "strange.png").

Thanks,

Christophe
Additional information
and documentation updates
See https://gitlab.onelab.info/gmsh/gmsh/-/issues/1327 for the related bug report in Gmsh.
TagsNo tags attached.
Test case number

Attached Files

  • two_volumes.brep (3,478 bytes)
  • strange.png (11,586 bytes)
  • EllispeAndSphere.png (50,853 bytes)
  • mesh.png (69,953 bytes)
  • two_volumes_with_freecad.brep (89,936 bytes)
  • two_volumes_union.brep (17,140 bytes)

Activities

geuzaine

2021-05-06 12:26

reporter  

two_volumes.brep (3,478 bytes)

geuzaine

2021-05-06 12:26

reporter  

strange.png (11,586 bytes)

mrbenson

2021-05-10 01:05

reporter   ~0100836

Last edited: 2021-05-10 01:27

But something wrong in your brep file, an error occurs when trying to open it with CAD Assisant.
I made the same example with freecad :
- the new brep file is imported in gmsh but when i activate swewing and fixing
 options, the sphere disappears.
-i get a mesh using netgen (included in freecad).

mrbenson

2021-05-10 01:07

reporter  

EllispeAndSphere.png (50,853 bytes)

mrbenson

2021-05-10 01:23

reporter  

mesh.png (69,953 bytes)

mrbenson

2021-05-10 01:24

reporter  

two_volumes_with_freecad.brep (89,936 bytes)

geuzaine

2021-05-10 10:07

reporter   ~0100840

Thanks for the testing!

Your "two_volumes_with_freecad.brep" geometry is however not the same as "two_volumes.brep" : you have a straight cylinder (instead of a tapered cylinder), and the sphere is at another location.

Attached is the file containing the union of the shapes from the original file ("two_volumes_union.brep"). Gmsh can produce a coarse mesh (similar to the one you obtained with Netgen) for this geometry. The issue is that if one refines, since the parametrization is self-overlapping, it will eventually lead to a self-overlapping mesh as well.

geuzaine

2021-05-10 10:07

reporter  

two_volumes_union.brep (17,140 bytes)

Issue History

Date Modified Username Field Change
2021-05-06 12:26 geuzaine New Issue
2021-05-06 12:26 geuzaine Assigned To => msv
2021-05-06 12:26 geuzaine File Added: two_volumes.brep
2021-05-06 12:26 geuzaine File Added: strange.png
2021-05-10 01:05 mrbenson Note Added: 0100836
2021-05-10 01:07 mrbenson File Added: EllispeAndSphere.png
2021-05-10 01:23 mrbenson File Added: mesh.png
2021-05-10 01:24 mrbenson File Added: two_volumes_with_freecad.brep
2021-05-10 01:27 mrbenson Note Edited: 0100836
2021-05-10 10:07 geuzaine Note Added: 0100840
2021-05-10 10:07 geuzaine File Added: two_volumes_union.brep
2021-05-10 11:34 kgv Summary Strange result of intersection => Modeling Algorithms - Strange result of intersection